Superheterodyne receiver



Sept. 15, 1936- w. VAN B. ROBERTS SUPERHETERODYNE RECEIVER Filed Feb. 15, 1935 udkba INVENTOR WALTER VAN B. ROBERTS ATTORNEY Patented Sept. 15, 1936 UNITED STATES PATENT OFFICE Walter van B. Roberts,

to Radio Corporation of America,

tion of Delaware Princeton, N. J assignor a corpora- Application February 15, 1933, Serial No. 656,793

8 Claims.

My present invention relates to superheterodyne receivers, and more particularly to a novel method of, and means for, simultaneously adjusting both the super-audible amplification of the receiver and local oscillator intensity.

It may be stated that it is one of the main objects of the present invention to provide a heterodyne receiver wherein there can be simultaneously varied the amplification of radio fre quency signal energy and heterodyne strength, this simultaneous variation particularly functioning as a volume control variation for the receiver.

Another important object of the present invention is to provide, in a superheterodyne type of radio broadcast receiver, a unitary means for simultaneously varying the gain of the radio frequency amplifier, the gain of the intermediate frequency amplifier, and the intensity of the output of the local oscillator.

Another object of the present invention is to provide a superheterodyne receiver which includes a means for substantially reducing the 10- cal oscillator strength when receiving local stations, thereby lessening radiation interference.

Still another object of the present invention is to provide a manual volume control device for a superheterodyne radio receiver, the device comprising a means for simultaneously varying the gain of the radio frequency amplifier and local oscillation strength without in any way affecting' the tuning of the local oscillator.

Still other objects of the present invention are to improve generally manual volume control devices for superheterodyne receivers, and particularly to provide for this type of receiver a volume control device which possesses considerable operating advantages when receiving local stations, is reliable in operation, and. is economically manufactured and assembled.

The novel features which I believe to be characteristic of my inventionv are set forth in particularity in the appended claims; the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawing in which I have indicated diagrammatically an arrangement whereby my invention may be carried into effect.

Referring now to the accompanying drawing wherein there is shown in diagrammatic manner a superheterodyne receiver, adapted to receive broadcast signals from 500 to 1500 kilocycles, it is to be noted that only so much of the circuit details of the receiver is shown as is necessary to a proper understanding of the construction and functioning of the present invention. The receiver, as is well known to those skilled in the art, comprises a grounded antenna circuit A which is coupled, as at M1, to the tunable input circuit of a radio frequency amplifier tube I of the screen grid type. The input circuit of the tube includes the variable tuning condenser 2, having its rotor elements grounded.

The screen grid and plate electrodes of tube I are adapted to be connected to appropriate sources of positive potential, and the plate circuit of tube I is coupled, as at M2, to the tunable input circuit of the first detector stage. The power supply source is not shown, but the resistor R1 from which the various positive potentials are derived is shown connected across this source. or course, those skilled in the art are well acquainted with the fact that such a source may be the output of the usual rectified alternating current filter circuit, or the output of a direct current supply system.

The high voltage end of the divider R1 is designated by the usual plus sign, While the low voltage side is designated by the customary minus sign. Across the divider R1 is connected a pair of resistors R and R2. The resistor R is a-variable one, while the resistor R2 is fixed. The negative side of the resistor R2 is grounded.

The screen grid and plate circuits of tube l, as well as the various other tubes, may be connected to the appropriate positive 'points along the divider R1. However, only such electrode connections will be described as are necessary to a proper understanding of this invention. The cathode of tube I is connected, 'as by a. lead 3, to the point 4 on the fixed resistor R2, and the lead 3 includes the normal bias resistor 1'1. A radio frequency by-pass condenser C3 is connected between the cathode of tube I and the grounded side of the variable condenser 2.

The first detector circuit includes in its output a circuit resonant to the operating inter* mediate frequency, and this circuit is coupled, as at M3, to the resonant input circuit of the intermediate frequency amplifier tube 5, of the screen grid type. The plate circuit of the tube 5, as well as the grid circuit of the tube, is fixedly tuned to the operating intermediate frequency. The output of the second detector is impressed upon the usual audio frequency amplifier. and the amplified audio signals are then reproduced in any customary manner.

The screen grid and plate circuits of tube 5 are connected to appropriate points of positive potential on the divider R1. The cathode of tube 5 is connected, through a lead 6, to a point I on the fixed resistor R2 which is more negative than the point 4. The lead 6 includes a bias resistor T2, and the high potential side of the bias resistor T2 is connected through the radio frequency bypass condenser C4 to the grounded side of the resonant input circuit of tube 5.

The local oscillator circuit of the receiver includes the screen grid tube 8 having its cathode connected to point 9 on the resistor R2, which point is positive with respect to points 4 and l, and this connection is made through a lead H] which includes the resistance II. The input circuit of the local oscillator tube 8 comprises an inductance coil l2 shunted by a variable tuning condenser l3, the rotor elements of the condenser I3 being grounded. The high potential side of the circuit I2, [3 is connected to the grid through a grid leak condenser M, and the condenser is shunted by a leak resistor H5. The plate of tube 8 is connected by a lead l6 to one side of the feed-back coil l1, and the opposite terminal of the feed-back coil I! is connected by a lead i8 to the point I9 on the divider R1. The screen grid of tube 8 may be connected to the desired positive point on the divider R1.

The feed back coil 11 is inductively coupled, as at M5, to the coil I2 to provide a feed-back circuit capable of producing local oscillations. Any desired type of radio frequency transmission network may be employed to impress the local oscil= lation energy from the local oscillator upon the first detector for the production of the intermediate frequency energy. In order to preserve simplicity of description, such a network has been shown in the drawing as comprising a pair of coils connected to form a link circuit, one of the coils 20 being coupled, as at Me, to the feed-back coil I1, and the other coil 21 being coupled, as at M1, to the coil in the input circuit of the first detector.

The resonant grid circuits of the radio frequency amplifier, first detector and local oscillator stages have their variable tuning condensers arranged for mechanical uni-control. For economical factory production these three variable condensers are made similar, and the rotor elements are mounted on a common operating shaft, conventionally designated by dotted lines 22 in the drawing. In order to constantly maintain the resonant grid circuit of the local oscillator differing from the resonant grid circuits of the radio frequency amplifier and first detector by the desired operating intermediate frequency, the usual shunt and series trimmer condensers may be employed in the circuit I2, I 3.

It is not believed necessary to complicate the present description and drawing by showing these trimmer condensers since this has been clearly shown by W. L. Carlson in U. S. Patent 1,740,331 of December 17, 1929. With these trimmer condensers the local oscillator variable condenser l3 may be adjusted to tune the local oscillator through a frequency range differing from the broadcast signal range at all times by the operating intermediate frequency. The manual volume control employed in the receiver described heretofore comprises the variable resistor R in series with the fixed resistor R2. The resistor It varies the bias on the radio frequency and intermediate frequency amplifier tubes and 5, preferably putting more bias on the tube I than on the tube 5. The resistors n and r2 provide the normal bias when the resistor R is adjusted to its maximum setting. As the magnitude of the resistor R is decreased to reduce the amplification of the radio frequency and intermediate frequency stages, the potential difference between the anode and cathode of the local oscillator tube 8 decreases, thus decreasing the local oscillator strength, and hence still further reducing the over-all gain of the receiver.

The advantages of having the volume control affect the local oscillator strength in addition to the amplifier biases may be summed up as fol lows:

(l) The reception of local broadcast signals, these signals being from powerful stations in the vicinity of the receiver, constitutes most of the activity of the average broadcast receiver. Since this must be accomplished with reduced oscillator strength, because when receiving strong local signals the resistor R would be adjusted to decrease the over-all gain of the receiver, radiation interference is greatly lessened.

(2) When receiving local stations, which means reduced over-all gain of the receiver, less heterodyne voltage is applied to the frequency changer tube, the first detector thereby giving less distortion or higher order effects.

(3) There is secured a greater control of the over-all gain of the receiver with the same variation of the usual volume control resistor B.

Other operating advantages will be obvious to those skilled in the art. It should be pointed out that the invention is not limited to the use of a single radio frequency amplifier tube and a single intermediate frequency amplifier tube, but it should be obvious that a plurality of radio frequency or intermediate frequency tubes may be employed. In this case, it is only necessary to multiply the present connections from these additional radio frequency and intermediate frequency amplifier tubes to the power supply resistor R2.

The local oscillator circuit shown is substantially stable with regard to frequency shift. That is to say, the local oscillator frequency will not shift appreciably with changing operating voltages. The grid leak condenser M should be small, and the leak resistor l5 of a relatively high resistance value. The cathode resistor II is preferably not by-passed. With this type of oscillator circuit any frequency shift which may occur due to plate impedance variation is substantially neutralized by the frequency shift due to the grid circuit impedance variation. In this way, the potential difference between the plate and cathode of the oscillator tube 8 may be varied without causing frequency drift of the local oscillator circuit.

While I have indicated and described one system for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organization shown and described, but that many modifications may be made without departing from the scope of my invention as set forth in the appended claims.

What I claim is:

1. In a superheterodyne receiver, a first detector, a second detector, an intermediate frequency amplifier coupling the first and second detectors, a radio frequency amplifier coupled to the input of the first detector, a local oscillator connected to the first detector, and a manual volume control device for said receiver comprising a common means for simultaneously varying the gain of said radio frequency and intermediate frequency amplifiers and the intensity of the local oscillations impressed on said first detector, said common means including an adjustable potential source connected to the oathode circuits of said oscillator and amplifiers.

2. In a superheterodyne receiver of the type including a radio frequency amplifier, a first detector, an intermediate frequency amplifier and a local oscillator circuit, a common potential source for the various circuits of said amplifiers and said local oscillator, and a common resistor means connected to the said potential source and said amplifier and local oscillator circuits for simultaneously increasing the gain of said amplifiers and the intensity of local oscillations impressed on the first detector.

3. In a superheterodyne receiver of the type including a tunable radio frequency amplifier circuit, a first detector circuit and local oscillator means for impressing locally produced oscillations on said first detector circuit means coupling the output circuit of said amplifier to the input circuit of said detector, a manual volume control means for said receiver comprising a unitary device for simultaneously decreasing the gain of said amplifier and the strength of said locally produced oscillations, said device consisting of an adjustable voltage source connected to the cathode circuits of the amplifier and oscillator.

4. In a heterodyne receiver of the type having a frequency changer circuit and a local oscillator coupled thereto for impressing local oscillations thereon, said oscillator comprising an electron discharge tube having grid and plate circuits, a manual volume control device for regulating the amplitude of the said oscillations consisting of a source of direct current energy, a resistor connected between said source and the plate of said oscillator, variable resistor means connected to the said source for varying the potential diffeernce between the cathode and plate of the oscillator and a resistor common to the grid and plate circuits of said oscillator and having one end connected to the low potential end of said variable resistor and its other end to said oscillator cathode.

5. In a heterodyne receiver of the type including a frequency changer circuit and a local oscillator coupled to the circuit for impressing local oscillations thereon, a device for regulating the amplitude of the said oscillations consisting of a source of direct current energy connected in the space current path of said oscillator, means connected to the said source for varying the potential difierence between the cathode and. anode of the oscillator, a. radio frequency amplifier having a tuned grid circuit, a cathode, and a plate circuit coupled to the changer circuit, a connection to ground from one end of said grid circuit, a resistor common to said plate and grid circuits and a connection between one end of said resistor and said varying means whereby regulation thereof simultaneously changes the bias of said amplifier grid.

6. In a superheterodyne receiver of a type including at least a radio frequency amplifier, intermediate frequency amplifier and local oscillator, a source of direct current energizing potential for said amplifiers and oscillator, and a single variable resistor connected between the said source and space current paths of said amplifiers and oscillator for adjusting the volume of the receiver.

7. In a superheterodyne receiver, a super-audible frequency amplifier and a local oscillator having plate and grid circuits, a source of direct current potential connected to the electrode circuits of the amplifier and oscillator, and a manual volume control device for the receiver comprising means to simultaneously adjust the oathode potential of the amplifier and the cathode potential of the oscillator a resistor common to the grid and plate circuits of said oscillator and a lead connecting one end of said resistor to one terminal of said volume control device.

8. In combination in a heterodyne receiver, a source of direct current voltage, a first resistor connected across the terminals of said voltage source, a second resistor connected across said voltage source and having at least a portion which is variable, a local oscillator having a cathode and plate, a connection between the plate and an intermediate point of said first named resistor, a radio frequency amplifier tube having a cathode, control grid and plate, a first detector having a tunable input circuit coupled to the plate circuits of said amplifier and oscillator, and connections between the cathodes of said oscillator and said amplifier tube and intermediate points of said second named resistor whereby adjustment of the variable portion thereof simultaneously increases the gain of said amplifier tube and the output voltage of said local oscillator.

WALTER VAN B. ROBERTS. 

